Cyclical process for the dehydrogenation of saturated hydrocarbons

ABSTRACT

A cyclical process is used to produce an olefinic hydrocarbon from paraffinic hydrocarbons. In the first step, the feed is contacted with a molybdenum-containing metal compound, e. g., iron, cobalt, or nickel molybdate, the step being conducted for a sufficient time to dehydrogenate the paraffinic hydrocarbon and at least partially reduce the molybdate to molybdite. In the second step, the molybdenum compound (at least partially reduced to the state of molybdite) is reoxidized to the molybdate form before it is contacted with additional paraffinic hydrocarbon, this reoxidation step being conducted by contacting the molybdite-containing compound with an oxygen-containing gas, essentially in the absence of paraffinic hydrocarbon. The first and second steps are repeated sequentially.

United States Patent Boutry et al.

[ 51 Sept. 19, 1972 I54] CYCLICAL PROCESS FOR THE DEHYDROGENATION OF SATURATED HYDROCARBONS [72] Inventors: Pierre Boutry, Port Marl); Jean Claude Daumas, Marly Le Roi; Roger Montarnal, Mareil Marly, all of France [73] Assignee: Institut Francais du Petrole des Carburants et Lubrifiants, Rueil Malmiason (I-Iauts de Seine), France [22] Filed: Oct. 21, 1969 [21] Appl. N0.: 868,205

[30] Foreign Application Priority Data Oct. 28, 1968 France ..68171682 [52] US. Cl. ..260/680 R, 260/683.3

[51] Int. Cl ..C07c 5/18 [58] Field of Search ..260/680 R, 683.3

[56] References Cited UNITED STATES PATENTS 3,050,572 8/1962 Masterton et al ..260/680 3,118,007 l/l964 Kronig et al. ..260/680 3,248,451 4/1966 Hughes ..260/68 3.3 3,375,291 3/1968 Callahan et al ..260/680 3,513,216 5/1970 Woskow ..260/680 3,600,457 8/1971 Milloy et al ..260/683.3

Primary Examiner-Paul M. Coughlan, Jr. Attorney-I. WilliamMillen [57] ABSTRACT A cyclical process is used to produce an olefinic hydrocarbon from parafiinic hydrocarbons. In the first step, the feed is contacted with a molybdenum-containing metal compound, e. g., iron, cobalt, or nickel molybdate, the step being conducted for a sufficient time to dehydrogenate the paraffinic hydrocarbon and at least partially reduce the molybdate to molybdite. In the second step, the molybdenum compound (at least partially reduced to the state of molybdite) is reoxidized to the molybdate form-before it is contacted with additional paraffinic hydrocarbon, this reoxidation step being conducted by contacting the molybdite-containing compound with an oxygen-containing gas, essentially in the absence of paraffinic hydrocarbon. The first and second steps are repeated sequentially.

12 Claims, No Drawings CYCLICAL PROCESS FOR THE DEHYDROGENATION OF SATURATED HYDROCARBONS The production of olefins and diolefins from paraffins of the same carbon structure is based essentially on simple catalytic dehydrogenation processes. This type of conversion involves a balanced reaction conforming to the laws of thermodynamics; in order to achieve industrially acceptable performances it is necessary to use rather unfavorable operating conditions: high temperature, lower hydrocarbon pressure.

These conditions in most cases result in a rapid deactivation of the catalyst and accordingly in the requirement of numerous regeneration steps which reduce substantially the life time of these catalysts.

In view of avoiding these numerous drawbacks, derived from the presence of a thermodynamic equilibrium, methods for selective removal of the hydrogen formed during the dehydrogenation, have been contemplated in order to displace the equilibrium towards a larger production of dehydrogenated compounds.

The most economical way therefor consists of introducing air or oxygen for converting the hydrogen to water by combustion. A number of processes has been proposed in the case of preparing diolefins by controlled oxidation of olefins in the presence of catalysts, but the rare examples of production of olefins and diolefins by oxidizing paraffms are generally characterized by poor performances, mainly as the result of the degradation reactions involving a complete combustion due to the simultaneous presence, in the gaseous reaction medium of hydrocarbons and oxygen.

It is an object of the present invention to provide a process for manufacturing olefins and diolefins from paraffin, said process being characterized by a first stage of contacting said paraffins with a metal compound or compounds mixture containing molybdenum at least in major part in the form of molybdate, said molybdate being selected from the'group consisting of iron, cobalt and nickel molybdates, followed with a second stage where the molybdate at least partially reduced to the molybdite form is reoxidized, before being again contacted with a new paraffin charge, at least partially to the molybdate form by contacting the same with an oxygen-containing gas, the oxidation of the paraffins being conducted in the absence of free oxygen and the oxidation of the molybdite being conducted in the absence of paraffins, said two stages being optionally carried out in the reverse order.

This process offers, with respect to the known processes for oxidation of paraffins, numerous advantages, mainly a high selectivity and a high yield even at a moderate reaction temperature and relatively high pressure, Moreover, due to the operation in the absence of oxygen it is possible to avoid secondary reactions of degradation which otherwise occur when hydrocarbons and oxygen are present in the reaction medium, said reactions resulting in the formation of the carbon dioxide in non-negligible amounts thereby leading on the one hand to the loss of a portion of the paraffins and on the other hand to temperature increases which are detrimental to the oxidation reaction.

The increase in selectivity is of particular interest in the case of branched hydrocarbon chains since the process of the invention avoids the breaking of the lateral chains.

The risks of explosions which might occur irrespective of the mean ratio oxygen/paraffin, are also avoided.

Moreover, according to the present process a small amount of molybdate as such or incorporated to such carriers as alumina, silica and the like, provides for the conversion of an almost unlimited amount of paraffins with excellent performances.

The paraffins which may be used according to the present invention are linear or branched paraffins containing from two to 10 and preferably from four to eight carbon atoms.

The process may be carried out by means of any apparatus whereby is achieved an alternate contact of the molybdate with the gaseous phase containing the paraffms, either alone or diluted with an inert gas such as nitrogen, carbon dioxide or steam, and thereafter of the reduced molybdate with the oxygen-containing gaseous phase, the process being by no way limited to the use of any particular apparatus.

It is obvious that the order of the two stages can be reversed, provided that there is fulfilled the condition according to which the molybdenum is initially, at least in major part (preferably in totality), in the form of molybdate when in the presence of paraffins and at least partly in the form of molybdite when in the presence of oxygen.

For instance the reaction can be carried out in a reaction vessel operated under dynamic conditions; reactants, injected under a pressure between 0.1 and 2 atmospheres, are successively introduced into the reac tion vessel containing the slid mass in the form of grains, extrudates or powder, having a size elected, in accordance with the type of operation: in a fixed bed for example there can be used particles of a diameter for instance between 0.1 and 50 mm; in a fluid bed, smaller diameters will be preferred in order to obtain a good stability of the bed, for instance diameters between 0.01 and 0.2 mm; in a moving bed, i.e. when the solid catalyst is circulated in the reaction vessel, intermediate sizes of, f.i.,'0.05 to 0.5 mm can be used.

All of these values are only given for illustrative pur poses since the sizes are to be selected according to each particular case of use, with consideration for the type of solid used, its mechanical properties, the operating conditions and the feature of the installation.

The successive introduction of the reactants, paraffin and oxygen or air, may be regulated by a system of automatically operated valves wherein each valve can be open only after the closure of the other valves.

In order to improve the safety of operation and avoid any risk of casual mixing of paraffin and oxygen, provision can be made for an intermediate supplemental injection of an inert gas (nitrogen, steam, carbon dioxide, for example).

The operating cycle will thus include the successive steps of l. Injecting paraffms on the molybdate, resulting in the production of olefins and diolefins and in at least a partial reduction of the molybdate to molybdite.

2. blowing off with an inert gas 3. injecting oxygen on the molybdite and oxidation of the molybdite to molybdate 4. blowing off with an inert gas 5. new cycle such as l The feeding system provides for sequential injections of gaseous reactants, paraffin, inert gas, oxygen or air for durations which are predetermined and adjustable in accordance with the experimental conditions. The velocity of the gaseous reactants is such that the flow rate, expressed in terms of the gas volume, under normal conditions of temperature and pressure, per volume of the contact mass and per hour, is, for example between 1,200 and 7,200 and preferably between 1,800 and 3,600 h.

The time of injection of the paraffins may be, for instance, between and 1,800 seconds and preferably between and 180 seconds.

The time of injection of oxygen (or air) may be for example between 2 and 60 and preferably between 10 and 30 seconds. I

The amount of inert gas to be injected for blowing off the reaction vessel depends on the volume of the installation and may accordingly vary within large limits; the time of injection can be made very short as compared to that of paraffin or oxygen, by use of a higher injection pressure. All the specific values of the pressures, flow rates and injection times are given only for illustrative purposes. 1n fact they are dependent on numerous factors and must generally be such as to provide preferably an equilibrium between the reaction of reduction of the molybdate during the stage of oxidizing paraffins and the reaction of oxidation of the molybdite when the same is contacted with an oxygen containing gas. According to the case, it may be of interest to use different flow rates for the paraffms and the oxygen, for example an oxygen flow rate higher than the paraffins flow rate.

The temperature of the reactions may be advantageously between 400 and 800 C., preferably between 450 and 550 C., the pressure being between 0.5 and 20 kglcm The following non-limitative examples are given for illustrative purposes. In all of the examples there has been used a molybdenum and cobalt compound prepared in the following manner:

0.143 mole of ammonium paramolybdate (NHQ MO O .,'4H O are dissolved in 500 ml of distilled water at 60 C. and 1 mole of hexahydrated cobalt nitrate Co(NO "'H O are dissolved in 125 ml of distilled water at 60 C. To the mixture ofthese two solutions is added dropwise under efficient stirring a solution of monoethanolamine of a normality so elected as to obtain a final pH value between 4.5 and 7.5.

The resulting precipitate is then filtered and dried in an oven at 1 10 C.

The solid, according to its designed conditions of use, is then crushed or extruded to the desired grain size.

The solid is thereafter calcinated, either under an oxidizing atmosphere (0 air) in order to obtain the solid at its higher oxidation state in the form of cobalt molybdate CoMoO.,, or under a reducing atmosphere (N H C.,H so as to obtain the solid at its lower oxidation state in the form of cobalt molybdite Co Mo O together with C00.

This calcination is conducted in both cases under identical temperature and pressure conditions, generally at a temperature between 300 and 800 C., preferably between 400 and 600 C., and under a pressure between 0.5 and 20 kg/cm EXAMPLE 1 There are used 10 g of the solid prepared as hereabove described with calcination under oxidizing atmosphere, in a tubular reactor operated under dynamic working conditions with successive introduction of the reactants as described before. The solid, in the form of grains having a diameter of 0.3 to 0.4 mm, is used in a fixed bed. The reaction temperature is 500 C., the pressure 2 kg/cm and the spatial velocity 3,000 h". There are successively injected n-butane for 2 mn, then nitrogen for 10 sec., thereafter oxygen for 30 sec. and finally nitrogen for 10 sec. The cycle duration was thus 2 mn 50 sec. After one cycle the results obtained were as follows Conversion C converted amount of n-butane amount of n-butane converted butadiene hourly yield:0.65 kg per kg of solid.

EXAMPLE 2 There are used the same conditions as in example 1 except for the injection time of each reactant. The injection time is 5 mn for n butane, 10 sec. for nitrogen, 50 sec. for oxygen and 10 sec. for the final nitrogen injection.

The cycle duration is thus 6 mn 20 sec The results obtained after 1 cycle were as follows C 22 S0438 44 SQ!!! 52 EXAMPLE 3.

The temperature and pressure conditions are the same as in example 1, the injection time of n-butane being brought to 15 mn. The spatial velocity of oxygen is brought to 3, 600 h, the injection time of oxygen being 1 mn. The cycle duration is thus 16 nm 20 sec.

The following results are obtained butadiene hourly yield 0.37 kg/kg of solid.

EXAMPLE 4 With experimental conditions identical to those of example 1 the results have been the following after cycles (duration: 4 h 43 mn) butadiene hourly yield 0.60 kg/kg of solid.

During 24 hours of experimentation in the conditions of example 1, the hourly yield was maintained between 0.67 ad 0.60 kg/kg ofsolid.

EXAMPLE 5 There are used 10 g of solid prepared as hereabove stated, with calcination under oxidizing atmosphere, the reaction temperature being 550 C., the pressure 2 kg/cm and the spatial velocity 3,000 h for n-butane and oxygen.

With a temperature of 5 50 C., an injection time of 2 nm for n-butane and 42 sec for oxygen, the injection time of nitrogen was sec. The following results have been obtained C: 35 $0518 36 So a =5 butadiene hourly yield 0.85 kg/kg of solid EXAMPLE 6 The experimental conditions of example 1 are unchanged except the reaction pressure which is 6 kglcm and the spatial velocity which is 6,000 h. The 1 results achieved have been the following C 30 83,38 40 S0436 52 butadiene hourly yield 1.56 kg/kg of solid EXAMPLE 7 There are used 10g of the solid prepared in the manner hereabove described. The injection is carried out in the same manner as in example 1. The feed consists of 2-methylbutane which is injected under conditions identical to those of example 1. The reaction temperature is 500 C. and the pressure 2 kg/cm The spatial velocity is 3,000 h". The following results have been obtained C 20 i-nmulene isoprene isoprene hourly yield 0.5 kg/kg of solid.

EXAMPLE 8 Example 6 is repeated but with a feed consisting of 2- methylbutane. The results obtained have been as follows C i-amulenc 21 isoprene isoprene hourly yield 1 1.13 kg/kg of solid.

EXAMPLE 9 Another method of reaction between the solid and the reactants has been used in this example. It consists of circulating the solid between two reactors one of which is fed with n-butane and the other with oxygen, the solid being in the form of a powder with a grain size between 0.05 and 0.15 mm. With a reaction temperature of 500 C., a spatial velocity of 3,000 h and a pressure of 2 kg/cm the following results have been obtained C 25 Sam, 46 S04E15 48 The butadiene hourly yield is 0.65 kg/kg of solid EXAMPLE 10 There has been prepared a solid cobalt molybdate" deposited on an alumina carrier. The preparation method is as follows there is prepared a mixture of solutions of ammonium paramolybdate and cobalt nitrate identical to that described above, and to the solution are added alumina grains whose textural features are so selected as to provide absorption of the solution by alumina. This results in a solid wherein cobalt molybdate represents percent by weight of the mixture thereof with alumina. The calcination conditions are the same as in example 1.

EXAMPLE 1 1 This example is given for comparison purpose. There are used 10 g of a solid prepared in the manner described in example 1, in a conventional tubular reactor operated under dynamic working conditions, with the solid in a powder form (grains diameter between 0.1 and0.2 mm) arranged in a fixed bed. The feed subjected to oxidation is a mixture containing 10 percent by volume of n-butane, 10 percent by volume of oxygen and ercent b golume of nitrogen, The reacion tempera ure 1s 0 C. and the spatial velocity 3,600 h. The following results have been obtained C=20 S0438 =26 Scgi =35 What we claim as this invention is: l. A cyclical process for manufacturing an olefinic hydrocarbon from a feed consisting essentially of paraf- 0 finic hydrocarbon containing four to five carbon atoms,

comprising a first step of contacting said feed essentially in the absence of free oxygen, with a molybdenum-containing metal compound wherein at least a major part of the molybdenum is initially in the form of a molybdate elected from the group consisting of iron, cobalt and nickel molybdates to dehydrogenate said paraffinic hydrocarbon and at least partially reduce said molybdate to molybdite, said first step being conducted for lO-l,800 seconds, and a second step of reoxidizing the molybdate at least partly reduced to the state of molybdite, before it is again contacted with a new paraffinic hydrocarbon feed, at least partly to the molybdate state by contacting it with an oxygen containing gas, essentially in the absence of paraffinic hydrocarbons, said second step being conducted for 2-60 seconds, and repeating said first and second steps.

2. A process according to claim 1, wherein the reaction temperature is between 400 and 800 C.

3. A process according to claim 1 wherein the pressure is between 0.6 and 20 kg/cm*.

4. A process according to claim 1 comprising al ternate injections, on the molybdenum compound in fixed bed, of the paraffinic hydrocarbon feed and the oxygen containing gas.

5. A process according to claim 1 wherein the molybdenum compound passes successively from an enclosure containing the paraffinic hydrocarbons to an enclosure containing the oxygen.

6. A process as defined by claim 1, said first step being conducted for 20 180 seconds and said second step being conducted for 10 30 seconds.

7. A process as defined by claim 1, further comprising the intermediate steps: blowing off the catalyst with an inert gas before said second step and blowing off the oxidized catalyst after said second step with an inert gas before said first step is repeated.

8. A process as defined by claim 1, wherein said molybdenum containing metal compound is cobalt molybdate.

9. A process as defined by claim 1 wherein said molybdenum-containing metal compound in the first step is initially completely in the form of a molybdate.

10. A process as defined by claim 4 further comprising the intermediate step of blowing off the catalyst with an inert gas after the first step is completed but before the second step commences.

l. 1. A process as defined by claim 4 further comprising the intermediate step of blowing off the oxidized catalyst with an inert gas after the second step is completed but before the first step if repeated.

12. A process as defined by claim 10 further comprising the intermediate step of blowing off the oxidized catalyst with an inert gas after the second step is completed but before the first step is repeated. 

2. A process according to claim 1, wherein the reaction temperature is between 400* and 800* C.
 3. A process according to claim 1 wherein the pressure is between 0.6 and 20 kg/cm2.
 4. A process according to claim 1 comprising alternate injections, on the molybdenum compound in fixed bed, of the paraffinic hydrocarbon feed and the oxygen containing gas.
 5. A process according to claim 1 wherein the molybdenum compound passes successively from an enclosure containing the paraffinic hydrocarbons to an enclosure containing the oxygen.
 6. A process as defined by claim 1, said first step being conducted for 20 - 180 seconds and said second step being conducted for 10 - 30 seconds.
 7. A process as defined by claim 1, further comprising the intermediate steps: blowing off the catalyst with an inert gas before said second step and blowing off the oxidized catalyst after said second step with an inert gas before said first step is repeated.
 8. A process as defined by claim 1, wherein said molybdenum containing metal compound is cobalt molybdate.
 9. A process as defined by claim 1 wherein said molybdenum-containing metal compound in the first step is initially completely in the form of a molybdate.
 10. A process as defined by claim 4 further comprising the intermediate step of blowing off the catalyst with an inert gas after the first step is completed but before the second step commences.
 11. A process as defined by claim 4 further comprising the intermediate step of blowing off the oxidized catalyst with an inert gas after the second step is completed but before the first step if repeated.
 12. A process as defined by claim 10 further comprising the intermediate step of blowing off the oxidized catalyst with an inert gas after the second step is completed but before the first step is repeated. 